1. Field of the Invention
The present invention is related to a grommet for a wire harness, in particular, to a grommet, into which a wire harness to be wired in an automobile is inserted and which is mounted in a through hole of a vehicle body panel, having an improved following deformability and a restoring force after deformation of the grommet.
2. Description of Related Art
Conventionally, when a wire harness wired in an automobile is inserted into a through hole of a vehicle body panel, a grommet, into which the wire harness is inserted, is mounted in the through hole of the vehicle body panel, and thus, the grommet protects a portion of the wire harness W/H passing through the through hole, and prevents water and dust from entering.
FIG. 5 shows an example of a known grommet. The grommet 1 shown in FIG. 5 has a small diameter cylinder portion 2, in which a wire harness W/H is tightly inserted, and a large diameter cylinder portion 4, in which an annular recessed portion 5 to be engaged with a through hole of a vehicle body panel (not shown), is provided. The small diameter cylinder portion 2 and the large diameter cylinder portion 4 are connected in an axial direction via a radially outward extending portion 3. A stretchable portion 6, which has a U-shaped cross-section and extends toward the large diameter cylinder portion 4 side in parallel to the axial direction, is provided at a portion where the radially outward extending portion 3 is connected to the small diameter cylinder portion 2. After the wire harness W/H is inserted into the grommet, an adhesive tape 8 for fixing the wire harness is wound around a portion from an outer peripheral surface of the wire harness, which is pulled out from the small diameter cylinder portion 2, to an outer peripheral surface of the small diameter cylinder portion 2, to fix them to each other.
When the grommet 1 is mounted into the through hole of the vehicle body, the grommet is pushed into the through hole, receives a pulling external force, and further receives a twisting or skewing external force. However, as shown in FIGS. 6A, 6B and 6C, the stretchable portion 6 follows the external force by compressing, stretching and bending, thereby absorbing the external force. Thus, the stretchable portion 6 prevents the large diameter cylinder portion 4 having the annular recessed portion 5 from receiving the external force. Accordingly, the annular recessed portion 5 is not separated from the through hole, and a gap between the through hole and the annular recessed portion 5 is not generated.
However, since the stretchable portion 6 is required to have a flexible deformability, the thickness of the stretchable portion 6 is thin and a restoring force after the deformation is weak. In particular, the grommet 1 is difficult to be restored after stretching or compressing deformation in the axial direction of the grommet 1. Therefore, the wiring path of the harness may be changed thereby. Further, the wire harness may interfere with other components, or a working space may be reduced due to the change in the wiring path.
In view of the above circumstances, Japanese Patent Application Publication No. 11-63313 discloses a grommet 100 as shown in FIGS. 7A and 7B. The grommet 100 has a small diameter cylinder portion 101, into which a wire harness 110 is tightly inserted, and a large diameter cylinder portion 103, in which an annular recessed portion 104 to be engaged with a through hole 109 of a vehicle body panel 108 is provided. The small diameter cylinder portion 101 and the large diameter cylinder portion 103 are connected via a circumferential wall portion 102. A stretchable portion 105, which extends toward the large diameter cylinder portion 103 side in parallel with an axial direction of the grommet 100, is provided at a portion where the circumferential wall portion 102 is connected to the small diameter cylinder portion 101. Reinforcing ribs 107 are provided in a concave portion 106 of the stretchable portion 105 on the small diameter cylinder portion 101 side, to connect between two side wall inner surfaces of the concave portion 106.
According to the grommet 100, a restoring force of the stretchable portion 105 after deformation is expected to be increased by the reinforcing ribs 107. However, the reinforcing ribs 107 restrict a stretching-and-compressing deformation of the stretchable portion 105 in the axial direction. Therefore, when the grommet 100 is inserted into the through hole 109, following deformability of the grommet 100 is reduced, and the insertion force into the through hole is not reduced. Further, a holding force to maintain the grommet 100 in the through hole is likely to be reduced.
Further, in the grommet shown in FIG. 5, when the deformation amount of the stretchable portion 6 increases, the adhesive tape 8 for fixing the wire harness, which is wound around a portion from the outer peripheral surface of the small diameter cylinder portion 2 to the outer peripheral surface of the wire harness W/H, is likely to be detached from an end portion, as shown in FIG. 6D. When the adhesive tape 8 is once detached, even if the stretchable portion 6 is restored to its original shape, the tape still remains detached, and the fixing force is weakened. Therefore, the positional displacement may occur in the mounting positions of the wire harness and the grommet. Further, when the operator grasps the grommet, the adhesive surface of the detached tape may stick to the operator's hand, and the detached tape may be completely separated from the grommet.